Water tube boilers with a steam production not exceeding45t per hour

84.02 - Steam or other vapour generating boilers (other than central heating hot water boilers capable also of producing low pressure steam); super-heated water boilers. 8402.11 8402.12 8402.19 8402.20 8402.90 - Steam or other vapour generating boilers : - - Watertube boilers with a steam production exceeding 45 t per hour - - Watertube boilers with a steam production not exceeding 45 t per how - - Other vapour generating boilers, including hybrid boilers - Super-heated water boilers - Parts (A) STEAM OR OTHER VAPOUR GENERATING BOILERS This group includes ap aratus for generating steam or other vapour (e.g., mercury vapour) to operate pnme movers &.g., steam turbines) or other machines using steam power e.g., steam hammers and pumps) or to supply steam to apparatus for heating, cooking, steri ising, etc., including steam generating boilers for central heating. I It includes separately presented boilers (e. ., locomotive boilers) even though they ma clearly be specially constructed to form an integra part of a particular machine, apparatus or ve icle. K k Steam boilers may be heated by means of a solid, liquid or gaseous hel, or by electricity. The desire to obtain a more efficient heatin effect, or quicker vaporisation fkom fuel-burning boilers has led to the production of boilers di ering in structure. The main types are : k (1) Firetube boilers (e.g., locomotive boilers), in which the body of the boiler is traversed by tubes through which the flue gases are conducted. (2) Watertube boilers, in which a system of watertubes is surrounded by the flue gases; the internal walls of some boilers are also formed of watertubes. (3) Hybrid boilers, which are generally a combination of types (1) and (2) above. In some boilers, the systems of tubes are connected by a collector to one or more generally cylindrical bodies which serve to store the water or separate the water from the vapour. In others, known as forced circulation boilers, there is sometimes no evaporation drum and the circulation of the water is accelerated by a pump. Boilers vary considerably in size. Small boilers are usually presented assembled, the various components being enclosed in a shell or mounted on a common base. The ,larger boilers comprise as a rule a number of separate elements for assembly on site, either w i h n a shell or withln a structure of brickwork. (B) SUPER-HEATED WATER BOILERS These are boilers in which the water is submitted to fairly high pressure so that it can be heated to a temperature far in excess of the normal vaporisation point (generally of the order of 180 "C or more). These boilers are structurally very similar to the boilers described in Part (A) above. The pressure required for their operation is obtained either by accumulatin steam in, for example, an evaporator drum, or in some cases, by means of an inert gas (genera ly nitrogen). The su erheated water produced in the boiler must be kept constant1 under pressure. It there ore circulates in closed circuit, starting fiom and returning to the boi er. Y f P Super-heated water boilers are used to provide heat, generally at a distance, to industrial plant (motor vehicle body aint drying tunnels, for instance), or to large groups of buildin s or district heatin schemes. In e latter case, heat is provided through heat exchangers in whic the superheate water (primary fluid) transfers calories to a secondary fluid that heats the premises. d % 5, In order to increase or regulate their ou ut or efficiency, the boilers of this heading are often equipped with a wide range of auxi iary apparatus. Such auxiliary apparatus includes econornisers, air pre-heaters, super-heaters, de-super-heaters, steam receivers, steam accumulators, soot removers, gas recoverers, watertube fire-box walls and other apparatus of heading 84.04, and feed water purifiers, de-aerators, de-gasifiers and softeners of heading 84.2 1. T'. Such auxiliaries are classified with the boilers in this heading when they are presented together therewith, whether they already form, or are designed to form subsequently, a whole with those boilers; if presented separately they are to be classified in their own appropriate headings. Similarly, and provided the are designed to form a whole therewith, grates presented with boilers are classified in this eading together with the boiler. In this respect, no distinction is made between grates already incorporated in boilers and those designed to be combined with boilers by means of a brickwork structure. K The heading excludes the types of boilers designed only for heating water to a temperature below its normal vaporisation point, and central heating hot water boilers of heading 84.03 (even if capable also of producing low pressure steam). PARTS Sub'ect to the general provisions regardin the classification of paf.ts see the General ~x&atory Note to Sectlon XVI), parts o f ti? e boilers of this headin are a so covered, e.g., boller bod~esand bases, internal assemblies for boilers consisting o tubes, watertube ca s, headers, boiler drums, steam domes, non-mechanical fire-boxes, inspection covers and fusl le plugs. f \ R Metal tubes or i es which have been bent or curved but not otherwise worked, presented unassembled, are not identi6fbL as parts of boilers and are therefore to be classified in Section XV.